The present invention relates to a disk array system and a method for controlling a disk array system.
In recent years, with the increase of storage capacity in disk array systems, the importance thereof in information processing systems becomes greater and greater. It is therefore essential to write data correctly in a requested position and detect falseness in read data in response to a data input/output request from an information processing apparatus or the like.
JP-A-5-150909 discloses a method in which two heads are provided in a magnetic disk unit, and identical data read from the two heads are compared with each other so as to enhance the reliability in writing and reading in the magnetic disk unit.
When the method disclosed in JP-A-5-150909 is applied to a disk array system, two heads have to be provided in each magnetic disk unit. Thus, the unit cost for manufacturing each hard disk drive increases. Therefore, requested is a method for enhancing the reliability in a hard disk drive without changing its physical structure, for example, without adding any head thereto.
In addition, in disk array systems, serial ATA or parallel ATA hard disk drives have come to be used as well as fiber channel hard disk drives. This is because serial ATA or parallel ATA hard disk drives are indeed inferior in reliability to fiber channel hard disk drives but lower in price. There is therefore a demand for development of a method for enhancing the reliability in hard disk drives other than fiber channel ones in a disk array system constituted by a combination of fiber channel hard disk drives and other hard disk drives conforming to the serial ATA standard or the like.